Interpretive Summary: The fall armyworm is an important agricultural pest in the western hemisphere. Two physically identical host strains of fall armyworm exist that differ in plant host usage and habitat distribution.Scientist of the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, performed extensive genetic studies on U.S. populations that identify genetic markers capable of distinguishing the two strains. This study examined whether the same genetic subgroups exist in Argentina and display similar host plant preferences. We found that the fall armyworms in Argentina are nearly identical to those found in the U.S. populations with respect to their genetic markers. The Argentine strains displayed biases in plant host distribution similar to that observed in the U.S. These results indicate that the biology and behaviors of fall armyworm demonstrated from studies of North American specimens are applicable to populations in Argentina.

Technical Abstract:
Fall armyworm is a major economic pest throughout the Western Hemisphere. Previous studies of populations in the southern United States, Brazil, and the Caribbean demonstrated the existence of two morphologically identical but genetically distinct host strains that can only be distinguished using genetic markers, including polymorphisms in the mitochondrial Cytochrome Oxidase I (COI) gene and in the Z-chromosome linked Triose phosphate isomerase (Tpi) gene. The strains differ in some physiological and behavioral characteristics, most notably their preference for different plant hosts, but are capable of hybridizing in the laboratory and in the field. These traits suggest that the strains are in the process of divergence, which may or may not be hemispheric in scope. The objective of this study was to determine whether the two strains are present in Argentina. It was found that the strain-diagnostic haplotypes of the COI and Tpi genes subdivided the Argentina population into two major groups. Each group displayed biases in their distribution among different plant hosts that were generally consistent with expected strain behavior. The overall results indicate that Argentina fall armyworm exhibit similar genetics and behavior to populations in the rest of the hemisphere. In addition, a comparison of haplotype frequencies indicated that the Argentina populations are similar to those in Brazil and Texas, consistent with possible interactions with these fall armyworm groups, but appeared to have had minimal exchanges with those from Puerto Rico or Florida.